A031529 Numbers k such that the continued fraction for sqrt(k) has even period and if the last term of the periodic part is deleted the central term is 31.

963, 967, 971, 983, 991, 1003, 1019, 1031, 1039, 1051, 1059, 1063, 1087, 3848, 3880, 3904, 3936, 3944, 4000, 4040, 4072, 4168, 4192, 4256, 4264, 4288, 4320, 4328, 4352, 8655, 8727, 8787, 8871, 8943, 9003, 9147, 9303, 9375, 9663, 9795, 15384, 15448

Offset

1,1

Links

Table of n, a(n) for n=1..42.

Mathematica

epct31Q[n_]:=Module[{cf=ContinuedFraction[Sqrt[n]], cf2}, If[Length[cf] ==1, cf2={1}, cf2=cf[[2]]]; EvenQ[Length[ cf2]] && cf2[[Length[cf2]/2]] == 31]; Select[ Range[16000], epct31Q] (* Harvey P. Dale, Dec 07 2012 *)

Crossrefs

Sequence in context: A393861 A158414 A031740 * A347884 A031709 A158413

Adjacent sequences: A031526 A031527 A031528 * A031530 A031531 A031532

Keyword

nonn

Author

David W. Wilson

Status

approved